Any reported cases of Ox Tox between 1.4 and 1.6?

[tursiops]

30 minutes of NDL

Let me restate.

Running a ppO2 higher than 1.2 in most recreational diving settings does not make sense, because the increase in NDL does not offer a practical benefit because the dives are gas limited when diving in a single tank. In my view the increased risk of CNS oxygen toxicity is greater than the slightly increased risk of DCS from running a lower ppO2 and the corresponding slight increase in inert gas tissue loading.

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The most common use of recreational Nitrox is to uptake less nitrogen, not to try and extend the bottom time. On a repetitive-dive day, less N2 is good.

 

[flymolo]

The most common use of recreational Nitrox is to uptake less nitrogen, not to try and extend the bottom time.

all of the padi marketing materials say otherwise

 

[Kendall Raine]

30 minutes of NDL

Let me restate.

Running a ppO2 higher than 1.2 in most recreational diving settings does not make sense, because the increase in NDL does not offer a practical benefit because the dives are gas limited when diving in a single tank. In my view the increased risk of CNS oxygen toxicity is greater than the slightly increased risk of DCS from running a lower ppO2 and the corresponding slight increase in inert gas tissue loading.

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Sorry. You did say NDL, not CNS. My bad.

 

[tursiops]

all of the padi marketing materials say otherwise

I'm talking about how Nitrox is actually used, not how it is marketed. There is no requirement to dive up to your NDL, and most don't while using Nitrox. That means less N2 uptake compared to doing the same dive on air.

 

[Nick_Radov]

There was an unexplained suspected Ox tox cave diving fatality back in 2007 were the pO2 was within the recommended 1.2-1.4ata range. Gas was Tmx 24/25 to max depth of 150 feet. Some cave divers went to using EAN30 instead of EAN32 for most 100-120ft deep cave dives after that.

2007-07-14 Incident – IUCRR

iucrr.org

The accident report seems a little mangled or incomplete. It states, "Tanks were filled with 24/25 trimix". Was that based on a direct gas analysis or tank labels or dive computer gas setting? There have been other incidents where the gas blender made an error and the diver trusted the sticker without analyzing. Assuming the mix information is accurate then pO2 at maximum depth of 160ft would be 1.4atm, although the average depth and pO2 was presumably less.

The description of the victim's symptoms seems consistent with a seizure. But assuming it was a seizure, was it caused by CNS oxygen toxicity or something else? Other medical conditions and medications such as Wellbutrin (bupropion) can increase seizure risk. Do we have the victim's medical history?

Was a postmortem toxicology report ever produced for the victim? There is some evidence that certain medications such as the decongestant pseudoephedrine could increase the risk of CNS oxygen toxicity but this isn't well understood. I'm not trying to blame the victim here or minimize the risk of oxygen exposure but this incident raises more questions than answers.

As a meta comment it's frustrating to reach these incident reports. The data is usually so inconsistent and fragmentary that it leaves us unable to analyze what really happened. I don't mean this as a criticism of the recovery divers; they're usually volunteers just trying to help, often at great personal risk and expense. But as a community we lack the data to determine root causes or make any systematic safety improvements. Like I think I know now what practices are safe or unsafe but when challenged I can't really back it up with hard data or even reliable anecdotes.

 

[johndiver999]

30 minutes of NDL

Let me restate.

Running a ppO2 higher than 1.2 in most recreational diving settings does not make sense, because the increase in NDL does not offer a practical benefit because the dives are gas limited when diving in a single tank. In my view the increased risk of CNS oxygen toxicity is greater than the slightly increased risk of DCS from running a lower ppO2 and the corresponding slight increase in inert gas tissue loading.

View attachment 868744

The assumption of "gas limited for recreational divers", is not applicable to a huge proportion of divers. I am generally not gas limited, and I run an 85 cu-ft tank, at 1.6 atm, and that is on the first of 3 dives for a typical day. Often, I run a much larger tank.

This sort of "rule of thumb" - "run 1.2 because you will run out of gas anyway" is arbitrary and over simplified.

 

[Seaweed Doc]

All else aside, if you are diving at 1.2 on a wall or other "no bottom" situation and your buddy for whatever reason runs into trouble and starts to sink, it'd be nice to know you can go after them without undue risk. On the other hand, if you push to 1.6 it's another matter....

That's a tree version of the forest "Leave a margin for the unanticipated event."

Back in the Dark Ages when I learned to dive, we were told 2.0 was the no go zone. So don't take that compressed air cylinder past 200 feet or so.

 

[crofrog]

The assumption of "gas limited for recreational divers", is not applicable to a huge proportion of divers. I am generally not gas limited, and I run an 85 cu-ft tank, at 1.6 atm, and that is on the first of 3 dives for a typical day. Often, I run a much larger tank.

This sort of "rule of thumb" - "run 1.2 because you will run out of gas anyway" is arbitrary and over simplified.

I know that qualifying words are hard for you, but I stated "most." Sure there are people taking bigger tanks and diving in different contexts

I invite you to provide a more robust analysis than you arbitrarily stating that my statement is arbitrary, but I doubt you will.

 

[johndiver999]

All else aside, if you are diving at 1.2 on a wall or other "no bottom" situation and your buddy for whatever reason runs into trouble and starts to sink, it'd be nice to know you can go after them without undue risk. On the other hand, if you push to 1.6 it's another matter....

That's a tree version of the forest "Leave a margin for the unanticipated event."

Back in the Dark Ages when I learned to dive, we were told 2.0 was the no go zone. So don't take that compressed air cylinder past 200 feet or so.

You can take air to 218 at 1.6, what are you talking about?

 

[johndiver999]

I know that qualifying words are hard for you, but I stated "most." Sure there are people taking bigger tanks and diving in different contexts

I invite you to provide a more robust analysis than you arbitrarily stating that my statement is arbitrary, but I doubt you will.

I don't need an analysis, I just know your statement doesn't apply to any of the many active divers I know.

I could make a similar "qualified" statement like: "Most divers probably shouldn't be below 60 ft", not sure how that is helpful or relevant to the discussion, but it is at least as valid as yours.